Ultrasonic energy is used in a variety of applications including, but not exclusive of, medical, industrial, and military applications. One common use for ultrasonic energy in manufacturing is for cleaning objects in liquids. In ultrasonic cleaning, a transducer, usually piezoelectric but sometimes magnetostrictive, is secured to or immersed in a cleaning tank to controllably impart ultrasonic vibration to the tank. The tank is filled with a cleaning liquid and parts are immersed into the liquid to be cleaned by ultrasonic agitation and cavitation. The ultrasonic energy itself can dislodge contaminants. Under certain conditions, the ultrasonic energy also creates cavitation bubbles within the liquid where the sound pressure exceeds the liquid vapor pressure. When the cavitation bubbles collapse, the interaction between the ultrasonically agitated liquid and the contaminants on the parts immersed in the liquid causes the contaminants to be dislodged.
In a typical ultrasonic cleaning system, the cleaning liquid is an aqueous solution, and parts immersed therein are cleaned via the aforementioned agitation and cavitation of the aqueous solution. Typically, the ultrasonic transducers transmit ultrasonic energy into the liquid-filled tank at frequencies of 18 kilohertz or greater, typically at a resonant frequency of the transducer and the load. The load includes the cleaning tank, the liquid in the tank, and the parts immersed in the liquid. When the ultrasonic transducer is driven at the resonant frequency of the load, the system is capable of delivering maximum power to the load.
The effectiveness of ultrasonic cleaning systems can be reduced by the presence of dissolved gases in the cleaning liquid. The presence of dissolved gases in the cleaning liquid used in ultrasonic cleaning systems may interfere with the cavitation that promotes the cleaning process. Typically, operators of ultrasonic cleaning systems will perform a degassing process for approximately ten minutes before commencing the actual cleaning. During this degassing process, the ultrasonic transducers are typically pulsed repeatedly for the entire ten minutes. Following the degassing process, the ultrasonic transducers can be switched to continuous operation needed for the cleaning operation.
Suboptimal liquid levels can also hinder the ultrasonic cleaning process. At certain liquid levels, the reflection of ultrasonic waves off of the surface of the liquid can create a destructive interference that reduces the energy effectively transferred from the ultrasonic transducers to the cleaning liquid. The ultrasonic energy which is transferred to the ultrasonic transducers, but which is not effectively transferred to the cleaning liquid is wasted. As a result, when suboptimal liquid levels are used, the cleaning times may need to be extended to achieve the same result that would be achieved in less time with optimal liquid levels. This increases cycle times and manufacturing costs for operators or ultrasonic cleaning systems.
It would therefore be desirable to have an ultrasonic cleaning system capable of providing the operator with an indication of the amount of dissolved gases in the cleaning liquid, and capable of indicating whether the cleaning liquid is at a suboptimal level. Embodiments of the invention provide such an ultrasonic cleaning system. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.